Adhesive compositions, particularly conductive adhesives, are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses include bonding of electronic elements such as integrated circuit chips to lead frames or other substrates, and bonding of circuit packages or assemblies to printed wire boards. Adhesives useful for electronic packaging applications typically exhibit properties such as good mechanical strength, curing properties that do not affect the component or the carrier, and rheological properties compatible with application to microelectronic and semiconductor components.
Recently, there has been an increased interest in b-stageable adhesives. A b-stageable material is a material that is usually dispensed onto a substrate as a liquid, then is b-staged to achieve a first solid phase. In this first solid phase the material acts like a thermoplastic, i.e., the material flows at an elevated temperature. At an even higher temperature, the material irreversibly crosslinks and becomes a thermoset material. The transition from the thermoplastic stage to the second solid phase is thermosetting. However, prior to that, the material behaves similarly to a thermoplastic material. Thus, such a material would permit low lamination temperatures while providing high thermal stability. In addition, b-stageable adhesives eliminate many of the storage, handling, dispensing, and processing issues that exist when dispensing an adhesive in a flowable form.
Moreover, a continuing challenge in the microelectronics packaging industry is the issue of shrinkage upon cure of the adhesives contained within the package. In many cases, the adhesive(s) used in a package shrinks when cured, thereby creating stress at the various interfaces inside the package. This leads to package failure and device failure and/or unreliability. Accordingly, there is a continuing need for b-stageable adhesives in the electronic packaging industry, and a particular need for adhesives with little to no shrinkage upon cure.